High density lipoprotein (HDL) is one of the five major groups of lipoproteins (chylomicrons, VLDL, IDL, LDL, HDL) which enable lipids like cholesterol and triglycerides to be transported.
HDL is discoidal in shape with a core of non-polar lipids, triaglycerols and cholesterol esters, and a surface monolayer of phospholipids and non-esterified cholesterol. Several apolipoproteins reside in HDL. The major apolipoprotein is apolipoprotein A-I (Apo A-I), which is a 28-kDa single polypeptide consisting of 243 amino acid residues. (Jay H. Stein, Internal medicine, Edition 5, Elsevier Health Sciences, 1998; 2515 pages).
The protective role of high density lipoprotein (HDL) has been confirmed in a number of studies, and plasma levels of HDL and its major protein Apo A-I are consistently inversely correlated with atherothrombotic risk (B G Choi et al., The role of high-density lipoprotein cholesterol in atherothrombosis, Mt Sinai J Med. 2006 July; 73(4):690-701).
Alpha-1 antitrypsin (AAT) is a 52 kD glycoprotein. Its principal function is to inhibit neutrophil elastase, preventing tissue damage. AAT deficiency leads to obstructive pulmonary diseases and liver dysfunction. Currently the most widely used treatment is an intravenous infusion of highly purified human AAT. Intravenous augmentation therapy has been demonstrated to be safe and weekly infusions of AAT result in plasma AAT concentrations that are above those considered protective. (R C Hubbard et al., Alpha-1 antitrypsin augmentation therapy for alpha-1 antitrypsin deficiency, Am J Med. 1988 Jun. 24; 84(6A):52-62).